Such vibrating gyroscopes are conventionally used in inertial systems intended for navigation, such as a gyrocompass, for example, which provides an angle of measurement relative to the reference direction of true north (heading).
Axisymmetric Coriolis Vibrating Gyroscopes (CVG), for example Hemispherical Resonance Gyroscopes (HRG) more generally referred to as type I, such as those described in ‘Type I and Type II micromachined vibrating gyroscopes’ by Andrei M. Shkel, pages 586-593, IEEE/ION (Institute of Electrical and Electronics Engineer/Institute Of Navigation), PLANS 2006, San Diego, Calif., USA, operate in an open loop and allow measuring an absolute angle of rotation on the basis of a measurement of an angle representing the geometric position of vibration of the gyroscope relative to measurement electrodes.
Such a gyroscope may also be used in a closed loop, by controlling the geometric position of vibration via a precession control as is described in particular in document FR 2 755 227.
In that case, the geometric position of vibration of the gyroscope is maintained in a fixed position, and the measurement is deduced from the control that must be applied to the gyroscope to maintain it in that fixed geometric position of vibration. This type of operation is also called “rate gyro feedback.” The values supplied by the physical measurement then no longer correspond to an angle but to a speed of rotation.
Whether used in open or closed loop, the measurements provided by these vibrating gyroscopes may contain errors which are particularly affected by the position of the vibration relative to the measurement electrodes. These errors therefore vary with the geometric position of vibration, and have the effect of degrading the level of precision of the values so measured. It is therefore useful to attempt to reduce these errors in order to improve the performance of this type of gyroscope.